In general, the use of inflatable crash bags for protecting drivers and passengers involved in vehicular accidents is widely known.
In early versions of such devices, a compressed gas such as air, carbon dioxide, or nitrogen was stored, in situ, in a pressure bottle or flask, the valving of which was activated by sensing means responsive to rapid change in velocity or direct impact.
Generally speaking, such devices have been found unsatisfactory because of slow crash bag-inflation rates and the problem and expense of maintaining a pressure bottle or flask at the required pressure level over an indefinite period of time.
As a result, stored gas systems have now been generally replaced by gas-generating propellant compositions, particularly exothermic gas-generating propellants.
A system of the latter type, however, must have a relatively short reaction time (10-60 milliseconds) to achieve the desired degree of bag inflation. In addition, it is very important that (a) the generated gas and reaction by products be essentially non toxic and non-corrosive; (b) the underlying exothermic reaction occur at a controlled rate to avoid generation of excessive heat capable of burning the passenger or weakening the crash bag; (c) the propellant composition retain both stability and reactivity for relatively long periods of time under at least normal driving conditions, including a wide range of ambient temperatures and shock; and (d) the amount of propellant, its packaging, and the bag itself must be very compact, light and storable within a steering column and/or dash panel.
Gas-generating crash bag propellant compositions known to the art include, for instance, an alkali metal azide combined with an alkali metal oxidant, together with an amide or tetrazole (U.S. Pat. No. 3,912,561); silicon dioxide with an alkali or alkaline earth metal plus a nitrite or perchlorate (U.S. Pat. No. 4,021,275); an alkali metal azide with a metal halide (U.S. Pat. No.. 4,157,648 ; a plurality of metal azides with metal sulfides, metal oxides and sulfur (U.S. Pat. No. 3,741,585); an alkali earth metal plus an azide with a peroxide, perchlorate or nitrate (U.S. Pat. No. 3,883,373); an alkali metal azide with a metal oxide (iron, titanium or copper) (U.S. Pat. No. 3,895,098); an alkali metal-or alkaline earth metal-azide with an oxidant consisting of iron oxide doped with up to 1 wt. % of nickel or cobalt oxide (U.S. Pat. No. 4,376,002); and an alkali-or alkaline earth metal-azide combined with an oxidant obtained by forming a hydrated gel of a suitable base and metal salt, which is thereafter dehydrated in the presence of a metal oxide of aluminum, magnesium, chromium, manganese, iron, cobalt, copper, nickel, cerium and various transition series elements (U.S. Pat. No. 4,533,416).
Generally, the most frequently used crash bag propellants contain an azide salt capable of producing nitrogen gas when reacted with an oxidizer component. Typical of such reactions are the following: EQU 2NaN.sub.3 +CuO.fwdarw.3N.sub.2 +Cu+Na.sub.2 O [1] EQU 6NaN.sub.3 +Fe.sub.2 O.sub.3 .fwdarw.9N.sub.2 +2Fe+3Na.sub.2 O [2]
in which elemental copper or iron and sodium oxide (Na.sub.2 O) are obtained as by-products.
While copper and iron have little toxicity in their elemental forms, Na.sub.2 O and similar alkali and alkaline earth metal oxides are potentially corrosive and/or toxic, owing to their caustic effect on tissue. In particular, nitrogen gas obtained by reacting metal azides and oxidizers, as above described, may additionally contain a substantial amount of alkali metal oxide by-product and corresponding hydroxides within readily breathed dust and aerosols.
It is an object of the present invention to obtain a safe alkali metal azide/oxidizer-type propellant composition capable of rapidly and consistently producing high quality nitrogen gas suitable for crash bag systems.
It is a further object to reduce corrosive properties of by-products generated by initiating the reaction of a crash bag propellant comprising a group 1(a)- or 2(a)-type metal azide component and an oxidizer component.